GK : THE WORLD

Wind is air in motion:
The chief cause of wind is difference in atmosphere pressure. One of the main reasons for differences in pressure is unequal heating of the air. From the high pressure belts the air flows outwards to the regions of low pressure. Owing to the rotation of the earth, the winds do not blow due north and south, but are deflected. In this deflection they obey Ferrel’s Law which states, “Any moving body on the earth surface including a current of air, tends to be deflected, the deflection being to the right in the northern hemisphere and to the left in southern hemisphere.” Land and seabreezed are local winds caused by the unequal heating of land and water. During the day the land becomes very much hotter than the sea, with the result that there is marked low pressure over the land. Thus the air over the sea flows rapidly loses heat, but the sea remains warm for a longer time. 

Thus at night, heavy cool air blows from the land to take the place of warm air rising over the sea. The monsoon or seasonal winds may be regarded as land and sea breezes on a large scale, in which the time-frame is a year instead of a day. This phenomenon is to be found in south-east Asia, but is especially marked in the subcontinent of India. A cyclone is a portion of the atmosphere in which the pressure is lowest in the centre. The winds blow inwards in anticlockwise direction in the Northern Hemisphere. In the Southern Hemisphere cyclonic winds blow in a clockwise direction in accordance with Ferrel’s Law. An anticyclone is a portion of the atmosphere in which the pressure is highest in the centre. The winds blow outwards in a clockwise direction in the Northern Hemisphere and in an anti-clockwise direction in the Southern Hemisphere.

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